WP function/filter for modifying http headers?That is very possible, but in this case it looks like the two hooks simply perform different functions. send_headers is an action that fires after the headers are sent while wp_headers is a filter on the headers that is applied before they are sent.

Advise on Templates for Custom Queries@ebohlman, I've been going through my unanswered questions and doing a little clean up. If you want to post your comment as an answer, I'll mark it as accepted. It was the info I needed.